This disclosure relates to offshore platforms for the exploration for, and production of, undersea petroleum deposits, and, in particular, to the various types of platforms genetically known as spars, whether of the classic, truss, or cell spar variety. More specifically, the present invention relates to a spar-type floating platform, of the type having a buoyant upper hull structure and a buoyant lower module that is detachably connected to the upper hull structure and that supports the mooring lines and/or a lower portion of one or more risers when the upper hull structure is detached from the lower module.
The development of sub-sea petroleum and natural gas deposits in Arctic deep water regions presents special challenges for offshore platform designs. Specifically, platforms in these regions must be able to resist local and global loads from ice in addition to loads imposed by wind, waves, and currents. In some cases, a platform must be moved to avoid contact with or collision with sea ice and icebergs.
One type of platform that has become widely used for the development of deep water deposits is the spar. The threat of ice would make it advantageous for the hull of the spar to be
detachable from its mooring and riser system to avoid impact from the ice. Also, the staged development of a particular deposit may be facilitated by changing out topside facilities (by the detachment of the upper hull structure) as development progresses. A spar system having a detachable hull structure is disclosed in U.S. Pat. No. 7,197,999, the disclosure of which is incorporated herein by reference in its entirety,